It is frequently desirable when copying documents to have the output image content aligned in a particular way on the page, for example to provide room for binding or to center the image content on the page. Some copiers (such as the Xerox 9700) have an user-selectable "margin shift" feature that allows offsetting the image content by either a fixed or variable amount in which the user can select (via a dial) some particular distance, and then that same distance will be applied to every page. However, this assumes that all of the originals being copied are similarly registered to work properly. Other copiers (such as the Canon CLC-500) offer an automatic center shift feature. However, this works by detecting a white border around the page being copied and thus moves the entire page, rather than the image content on the page. Both of these examples are instances of absolute registration, i.e. image displacement to a fixed, known position. Neither of the example solutions is capable of dealing with a related problem, relative registration. In relative registration, it is desired to find the best match of a given image content to some reference image content, without any a priori information as to the position of the reference image content.
A simple, relatively inexpensive, and accurate approach to register images in such printing systems has been a goal in the design, manufacture and use of printers. The need to provide accurate and inexpensive registration has become more acute, as the demand for high quality, relatively inexpensive images has increased.
Various techniques for registering images have hereinbefore been devised as illustrated by the following disclosures, which may be relevant to certain aspects of the present invention: